Float arrangement

ABSTRACT

The present invention relates to a float which is provided with at least one hoist drum for a hoisting wire from a hoist. The float is provided with at least one suspension drum for a suspension wire to a suspension body. The hoisting drum and the suspension drum are rotationally coupled to each other and the wires are arranged in such a way on the drums that the suspension wires are reeled in when the hoisting wires are reeled off the hoisting drums and vice versa.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an arrangement which serves to facilitate thelaunching of and taking aboard surface referenced systems. A primary useof the arrangement according to the invention is with floats adapted tocarry air guns for marine seismic prospection.

Even though this arrangement has been particularly developed for seismicuses, it is near at hand to assume that it may also be used in otherfields, for example within offshore oil activity and in the fisheries.

More particularly this invention is directed to a float arrangementadapted to be launched in water and to be retracted, respectively, bymeans of a hoist, the float being adapted to carry at least onesubmersible body suspended from the float by means of a wire.

2. Description of the Prior Art

A practical form of such a float having a number of submersible bodiesin the form of air guns is described in European Patent Application No.EPC 81.902753.3.

SUMMARY OF THE INVENTION

What is novel and specific to the arrangement according to the presentinvention in the first place consists therein that the float is providedwith at least one hoisting drum for a hoist wire from the hoist, that,moreover, the float is provided with at least one suspension drum forthe suspension wire to the submersible body, that the hoisting drum andthe suspension drum are rotationally coupled to each other, and that thewires are arranged in such a way on the drums that the suspension wiresare reeled in when the hoist wires are reeled out from the hoistingdrums, and vice versa.

In short, the solution stated here involves that submersible bodies forexample in the form of air guns, may be hoisted to a position closelyunderneath the float which then in its turn may be lifted by means of ahoist, for example a telescoping boom on a seismic prospection vessel.The boom may then be retracted onto the deck of the vessel with thefloat and the air guns without having to pull these onboard over aslipway and further along the deck. This means that the equipment maymore easily be lauched and retracted at the same time as reducing to ahigh degree the stresses imposed upon such equipment when pulled up fromthe water to the deck via a slipway or the like.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention shall be explained more closely in the following withreference to the drawing, in which:

FIG. 1 schematically shows an arrangement according to the invention inside view, and

FIG. 2 shows a float in the arrangement, seen partly in section from oneend and at an enlarged scale.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a bouy or body 10 in the form of an elongated float or thelike which has been lowered to the water surface 100 by means of a hoistin the form of a boom 1 having hoisting wires 2 and 3. Besides, in theposition shown air guns 11, 12 and 13 have been lowered from the float10 and are suspended in the positions shown by means of suspension wires14, 15 and 16. The remaining four air guns with their wires being shownin FIG. 1, correspond completely to the above air guns 11, 12 and 13 andshall not be described in detail in the following.

For the towing of the float with air guns during seismic prospection thewires 2 and 3 are detached from the boom 1 so that the float 10 may bebrought into a desired position with respect to the vessel, determined,inter alia, by the length of the towing wire. According to commonpractice a number of floats with associated air guns may be towed incertain configurations in order to obtain defined sound radiationpatterns from the air guns as a whole. At 30 and 40 there are indicatedhoses and conduits for supplying compressed air and control signals etc.to the air guns.

On the float 10 there is mounted an axle 4 for example by means ofbearing supports 21, 22 and 23 and the complete axle 4 may besub-divided into two sections 4a and 4b by means of a flexible coupling19. Such sub-division of the axle into two or more sections may bepractical depending upon the total length of the axle and upon thedesign of the float.

In the first place the axle 4 carries two hoisting drums 5 and 6 for therespective hoisting wires 2 and 3. Moreover, the axle carries a total ofseven suspension drums of which there is here referred to the threesuspension drums 7, 8 and 9 for the respective air guns 11, 12 and 13with associated suspension wires 14, 15 and 16. For their respectivedrums these wires are passed through vertical channels 24, 25 and 26,respectively, in the float. It is obvious that when the drawing shows atotal number of seven air guns, this is only a pure example, since thenumber of air guns in such an arrangement may of course be larger orsmaller than this. In other uses it may be contemplated that it would beof interest to have only one single submersible body and that it wouldbe sufficient with one single hoisting wire. In such case the float willonly comprise one hoisting drum and one suspension drum.

The manner of operation of the arrangement as illustrated in thedrawing, is as follows:

When the equipment is to be launched from the vessel, the hoisting wires2 and 3 are tight and the hoisting drums 5 and 6 more or less empty ofwire, whereas on the other hand the suspension drums 7, 8 and 9 havingthe associated wires 14, 15 and 16 full reeled in so that the air guns11, 12 and 13 are suspended closely underneath the float 10, i.e. inengagement with the bottom thereof.

The hoist boom 1 has a cantilevered position with respect to the vessel,and the float 10 is lowered by paying out the hoist wires 2 and 3. Whenthe float has reached the water, continued paying-out of the hoistingwires means that the air guns 11, 12 and 13 start to sink from the float10. This causes rotation of the axle 4 so that the suspension wire isreeled out from the respective drums 7, 8 and 9, whereas the hoistingwires 2 and 3 are reeled in onto the hoisting drums 5 and 6.

When the suspension drums 7, 8 and 9 have become empty or the loweringof the air guns 11, 12 and 13 is stopped in some other way, these willbe suspended in their correct depth under the float 10. The hoistingwires 2 and 3 will be reeled onto the hoisting drums 5 and 6 and bymeans of shackles these wires may be disconnected from the hoist andfastened in a suitable manner to the float 10 or to a towing wire, sothat the air gun array on the float may be brought into a desiredposition in the water for the towing. The boom 1 may then be retractedfor fetching possible additional floats which shall be used in thearrangement of air guns to be used for the seismic prospectionconcerned.

When the float 10 with associated air guns shall be taken aboard aftercompletion of the task, the procedure will be the opposite of what hasbeen sketched above, since the hoisting wires 2 and 3 must be connectedto the hoist, i.e. to wire ends which have been pulled out on the boom 1so that hoisting may be commenced by means of a winch onboard thevessel. During hauling-in of the hoisting wires 2 and 3 these will firstbe reeled off from the hoisting drums 5 and 6 so that the axle 4 rotatesand thereby causes the suspension drums 7, 8 and 9 to reel in thesuspension wires 14, 15 and 16 until the air guns have been lifted to aposition closely underneath the bottom of the float 10. When the gunshave arrived at this position, continued hauling-in of the hoistingwires 2 and 3 means that the float 10 is lifted from the water andpossibly to a position closely underneath the boom 1. Then the boom 1may be retracted over the deck of the vessel and the whole equipmentwith float and air guns may be parked and disconnected so that the boomwill be ready for the possible hauling-in of other floats withassociated air guns.

From the above it should be apparent that the handling of such floatswith submersible bodies is provided for in a comparatively simple andpractical manner. When the submersible bodies have been elevated bymeans of the wires 14, 15 and 16 on the drums 7, 8 and 9, the wholeequipment has been transformed to a comparatively compact unit which canwithout significant problems be removed and stored during the operationof for example seismic prospection vessels. The function described hasbeen obtained without the necessity of having motor installations of thefloat. The whole arrangement is very simple and reliable, conforming tothe requirement to such equipment for use at sea, both in oil activityas for example for fishery purposes.

As explained above the submersible body or the air gun itselfconstitutes a stop member being in cooperation with the bottom of thefloat 10, adapted to arrest the suspension wire against continuedreeling when hauling-in the float. Specific stop members may becontemplated for the same purpose, depending upon, inter alia, the typeof submersible body concerned and the design of the float.

The rotational coupling of the respective drums as shown in the drawing,is effected directly through the continuous axle 4. Obviously, there maybe thought of more complicated embodiments in which for example axlesections may be arranged at an angle to each other and in which there isused a gear transmission between the drums. The same fundametal functionwill also be obtainable in such embodiments. Thus, with a geartransmission the rate of rotation and thereby the velocity of reeling-inand reeling-off, respectively, may be separately adjustable for theindividual drums. Without such gear transmission, variations of the drumdiameters may also be utilized as a means of obtaining specific velocityrelationship desired for the various wires involved in the arrangement.Normally, however, an arrangement having two or more hoisting wires froma hoist means, will provide for associated hoisting drums being designedfor the same wire velocity. In such case it is an advantage in practicethat these hoisting drums have the same diameter.

When employing an elongated float as for example shown in the Norwegianpatent application referred to initially, it is convenient to arrangethe suspension drums with axial alignment both mutually and with respectto the hoisting drums. The common drum axle runs in the longitudinaldirection of the float in such an embodiment. Preferably, in thisembodiment all wires are arranged to lie in the same vertical plane,which may be located approximately centrally of the float 10.

FIG. 2 shows more in detail the arrangement of the axle section 4a withdrum 7 by means of the support 21 on the deck of the float 10. Asuspension wire (not shown) may be passed from the drum 7 through theinterior of the float 10 in the channel 24 which is open through thebottom or the keel of the float.

In a particularly simple and practical embodiment the suspension drumsare designed with the same diameter as the hoisting drums.

We claim:
 1. Float arrangement for marine seismic prospection comprisingan elongate float and at least two submersible seismic sources carriedthereby, said float and said seismic sources being adapted to belaunched into water and lifted therefrom, respectively, as a unit bymeans of a hoist above the water surface, and said float being adaptedto be towed on the water surface with said seismic sources suspendedfrom the float by a respective suspension wire, further comprising atleast two hoisting drums on the float and each with an associatedhoisting wire from the hoist, a suspension drum on the float for eachsuspension wire, said hoisting drums and said suspension drums beingrotationally coupled to each other and said wires being arranged in sucha way on the drums that the suspension wires are reeled in when thehoisting wires are reeled off from the hoisting drums and vice versa,said seismic sources being adapted to constitute stop members forcooperation with the bottom of the float to arrest the suspension wiresagainst continued reeling when the float is hauled in by means of thehoist, and stop means being provided for stopping said seismic sourceswhen reeled out, at a predetermined distance below the float. 2.Arrangement according to claim 1, wherein there is for each suspensionwire provided a vertical channel passing through the float (10). 3.Arrangement according to claim 1, wherein it comprises two hoistingwires with associated hoisting drums which are rotationallyinterconnected and preferably have the same diameter.
 4. Arrangementaccording to claim 3, wherein the float has an elongate shape and isprovided with two or more suspension drums which are in axial alignmentmutually as well as with respect to the hoisting drums, and also in thelongitudinal direction of the float.
 5. Arrangement according to claim4, wherein it comprises a common axle for all drums and being preferablysubdivided into sections by means of at least one flexible coupling. 6.Arrangement according to claim 1, wherein the suspension drums have thesame diameter as the hoisting drums.
 7. Arrangement according to claim4, wherein all wires are adapted to lie in the same vertical plane,preferably approximately centrally of the float.
 8. Float arrangementfor marine seismic prospection comprising an elongate float and at leasttwo submersible seismic sources carried thereby, said float and saidseismic sources being adapted to be launched into water and liftedtherefrom, respectively, as a unit by means of a hoist above the watersurface, and said float being adapted to be towed on the water surfacewith said seismic sources suspended from the float by a respectivesuspension wire, further comprising at least two hoisting drums on thefloat and each with an associated hoisting wire from the hoist, asuspension drum on the float for each suspension wire, said hoistingdrums and said suspension drums being rotationally coupled to each otherand said wires being arranged in such a way on the drums that thesuspension wires are reeled in when the hoisting wires are reeled offfrom the hoisting drums and vice versa, said seismic sources beingadapted to constitute stop members for cooperation with the bottom ofthe float to arrest the suspension wires against continued reeling whenthe float is hauled in by means of the hoist, and stop means beingprovided for stopping said seismic sources when reeled out, at apredetermined distance below the float, said submersible seismic sourcesbeing free of any positive buoyancy so that the respective suspensionwire is reeled out when each of said submersible sources sinks by itsown weight into the water.